The present invention relates to orthodontic face bows, and in particular to an orthodontic face bow which provides a secondary orthodontic correction to the anterior lower teeth of the wearer.
Orthodontic face bows, such as that illustrated in the patent to Case, U.S. Pat. No. 862,881, are used to make certain types of orthodontic corrections in which an outside source of a rearwardly directed force is desired. The face bow includes a frame which fits around the face of the wearer and connects to a headstrap which biases the frame rearwardly relative to the head of the wearer. The frame connects to arch members inside the wearer's mouth which fit around the exterior of the upper teeth (or, on rare occasions, the lower teeth) of the wearer and engage buccal tubes fixed to the posterior upper teeth. The face bow thus provides a rearward force on the posterior upper teeth of the wearer to correct a malocclusion without unwanted reactionary forces on other portions of the mouth.
In many situations, it is also desirable to use the face bow for the secondary purpose of providing a rearwardly directed force on the anterior lower teeth of the wearer. This is now usually done in a jerry-rig style by simply hooking rubber bands from the buccal tubes engaged by the face bow to braces attached to the anterior lower teeth. The rubber bands are tension members which induce the desired rearwardly directed force on the anterior lower teeth.
The problem with using currently available face bows to provide a secondary correction for the anterior lower teeth as discussed above is that the force provided by the tension member is not precisely rearwardly directed. Since the tension member runs from the posterior upper teeth to the anterior lower teeth, a downward force component is exerted on the posterior upper teeth, and an upward force component is exerted on the anterior upper teeth. These vertical force components are normally termed "extrusion vectors", and can cause unwanted tooth movement which interferes with the desired orthodontic correction.
U.S. Pat. No. 3,131,953 to Asher illustrates the use of an upturned hook on the arch member of the face bow to facilitate attachment of a rubber band thereto. However, as illustrated in the Asher patent, rubber bands emanating from such a hook should only be connected to the anterior upper teeth--connection to the anterior lower teeth would result in the same unwanted extrusion vectors discussed above.